I want the voice to perform a line differently

You can regenerate the performance:

1. Pause rehearsal in Run Lines.
2. Tap the line → three dots ⋯ → Edit Line.
3. Add or remove a full stop at the end of the line.
4. Tap Save.
5. Go to the previous line and press Play—you'll see "Preparing Audio 0/1 Line." That refreshes the delivery for that line.

(We're developing more expressive controls soon, sit tight)